Editing Haidinger's brush (section)

==Seeing Haidinger's brush==
[[File:Haidinger's Brush (as demonstrated on Wikipedia's main page).jpg|thumb|260px|Simulated appearance of a computer screen viewed through a polarizer, showing typical size and intensity of Haidinger's brush]]

Many people find it difficult to see Haidinger's brush initially. It is very faint, much more so than generally indicated in illustrations, and, like other [[stabilized images]], tends to appear and disappear.

It is most easily seen when it can be made to move. Because it is always positioned on the [[macula]], there is no way to make it move laterally, but it can be made to rotate, by viewing a white surface through a rotating polarizer, or by slowly tilting one's head to one side.

To see Haidinger's brush, start by using a polarizer, such as a lens from a pair of polarizing sunglasses. Gaze at an evenly lit, textureless surface through the lens and rotate the polarizer.

An option is to use the polarizer built into a computer's [[liquid crystal display|LCD]] screen. Look at a white area on the screen, and slowly tilt the head (this method generally works only with LCDs, as most other [[Electronic visual display|electronic visual display]] technologies do not emit polarized light).

It appears with more distinctness against a blue background. With practice, it is possible to see it in the naturally polarized light of a blue sky. [[Marcel Minnaert|Minnaert]] recommended practicing first with a polarizer, then trying it without.<ref>Minnaert, M. G. J. (1940). Light and colour in the open air  (H. M. Kremer-Priest, Trans.). London: G. Bell and Sons.</ref> The areas of the sky with the strongest polarization are those 90 degrees away from the sun. Minnaert said that after a minute of gazing at the sky, "a kind of marble effect will appear. This is followed shortly by Haidinger's brush." He commented that not all observers see it in the same way. Some see the yellow pattern as solid and the blue pattern as interrupted, as in the illustrations on this page. Some see the blue as solid and the yellow as interrupted, and some see it alternating between the two states.